The Darrieus wind turbine is a type of
vertical axis wind turbine
A vertical-axis wind turbine (VAWT) is a type of wind turbine where the main rotor shaft is set transverse to the wind while the main components are located at the base of the turbine. This arrangement allows the generator and gearbox to be ...
(VAWT) used to generate
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
from
wind energy
Wind power or wind energy is mostly the use of wind turbines to electricity generation, generate electricity. Wind power is a popular, sustainable energy, sustainable, renewable energy source that has a much smaller Environmental impact of wi ...
. The
turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
consists of a number of curved
aerofoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
blades mounted on a rotating shaft or framework. The curvature of the blades allows the blade to be stressed only in
tension
Tension may refer to:
Science
* Psychological stress
* Tension (physics), a force related to the stretching of an object (the opposite of compression)
* Tension (geology), a stress which stretches rocks in two opposite directions
* Voltage or el ...
at high rotating speeds. There are several closely related wind turbines that use straight blades. This design of the turbine was patented by
Georges Jean Marie Darrieus
Georges Jean Marie Darrieus (24 September 1888 – 15 July 1979) was a French aeronautical engineer in the 20th century. He is perhaps most famous for his invention of the Darrieus rotor, a wind turbine capable of operating from any direction and ...
, a
French aeronautical engineer
Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is si ...
; filing for the patent was October 1, 1926. There are major difficulties in protecting the Darrieus turbine from extreme wind conditions and in making it self-starting.
Method of operation
In the original versions of the Darrieus design, the aerofoils are arranged so that they are
symmetrical
Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definiti ...
and have zero
rigging angle, that is, the angle that the aerofoils are set relative to the structure on which they are mounted. This arrangement is equally effective no matter which direction the wind is blowing—in contrast to the conventional type, which must be rotated to face into the wind.
When the Darrieus rotor is spinning, the aerofoils are moving forward through the air in a circular path. Relative to the blade, this oncoming airflow is added vectorially to the wind, so that the resultant airflow creates a varying small positive
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
to the blade. This generates a net force pointing obliquely forwards along a certain "line of action". This force can be projected inwards past the turbine axis at a certain distance, giving a positive torque to the shaft, thus helping it to rotate in the direction it is already travelling in. The aerodynamic principles which rotate the rotor are equivalent to that in autogiros, and normal helicopters in autorotation.
As the aerofoil moves around the back of the apparatus, the angle of attack changes to the opposite sign, but the generated force is still obliquely in the direction of rotation, because the wings are symmetrical and the
rigging angle is zero. The rotor spins at a rate unrelated to the windspeed, and usually many times faster. The energy arising from the torque and speed may be extracted and converted into useful power by using an
electrical generator
In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...
.
The aeronautical terms
lift
Lift or LIFT may refer to:
Physical devices
* Elevator, or lift, a device used for raising and lowering people or goods
** Paternoster lift, a type of lift using a continuous chain of cars which do not stop
** Patient lift, or Hoyer lift, mobile ...
and
drag are, strictly speaking, forces across and along the approaching net relative airflow respectively, so they are not useful here. The forces at play are rather
tangential force, which pulls the blade around, and radial force, which acts against the bearings.
When the rotor is stationary, no net rotational force arises, even if the wind speed rises quite high—the rotor must already be spinning to generate torque. Thus the design is not normally self-starting. Under rare conditions, Darrieus rotors can self-start, so some form of brake is required to hold it when stopped.
One problem with the design is that the
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
changes as the turbine spins, so each blade generates its maximum torque at two points on its cycle (front and back of the turbine). This leads to a sinusoidal (pulsing) power cycle that complicates design. In particular, almost all Darrieus turbines have
resonant modes where, at a particular rotational speed, the pulsing is at a natural frequency of the blades that can cause them to (eventually) break. For this reason, most Darrieus turbines have mechanical brakes or other speed control devices to keep the turbine from spinning at these speeds for any lengthy period of time.
Another problem arises because the majority of the mass of the rotating mechanism is at the periphery rather than at the hub, as it is with a propeller. This leads to very high
centrifugal stresses on the mechanism, which must be stronger and heavier than otherwise to withstand them. One common approach to minimise this is to curve the wings into an "egg-beater" shape (this is called a "
troposkein {{Short description, Momentum curve of a rope
In physics and geometry, the troposkein is the curve an idealized rope assumes when anchored at its ends and spun around its long axis at a constant angular velocity. This shape is similar to the sha ...
" shape, derived from the Greek for "the shape of a spun rope") such that they are self-supporting and do not require such heavy supports and mountings. See. Fig. 1.
In this configuration, the Darrieus design is theoretically less expensive than a conventional type, as most of the stress is in the blades which torque against the generator located at the bottom of the turbine. The only forces that need to be balanced out vertically are the compression load due to the blades flexing outward (thus attempting to "squeeze" the tower), and the wind force trying to blow the whole turbine over, half of which is transmitted to the bottom and the other half of which can easily be offset with
guy wires
A guy-wire, guy-line, guy-rope, or stay, also called simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A thi ...
.
By contrast, a conventional design has all of the force of the wind attempting to push the tower over at the top, where the main bearing is located. Additionally, one cannot easily use guy wires to offset this load, because the propeller spins both above and below the top of the tower. Thus the conventional design requires a strong tower that grows dramatically with the size of the propeller. Modern designs can compensate most tower loads of that variable speed and variable pitch.
In overall comparison, while there are some advantages in Darrieus design there are many more disadvantages, especially with bigger machines in the MW class. The Darrieus design uses much more expensive material in blades while most of the blade is too close to the ground to give any real power. Traditional designs assume that the wing tip is at least 40 m from ground at lowest point to maximize energy production and lifetime. So far there is no known material (not even
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
) which can meet cyclic load requirements.
Giromills
![Marine Board Hobart 20171120-029](https://upload.wikimedia.org/wikipedia/commons/2/26/Marine_Board_Hobart_20171120-029.jpg)
Darrieus's 1927
patent
A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
also covered practically any possible arrangement using vertical airfoils. One of the more common types is the H-rotor,
also called the Giromill or H-bar design, in which the long "egg beater" blades of the common Darrieus design are replaced with straight vertical blade sections attached to the central tower with horizontal supports. This design is used by Shanghai based MUCE.
Cycloturbines
Another variation of the Giromill is the Cycloturbine, in which each blade is mounted so that it can rotate around its own vertical axis. This allows the blades to be "pitched" so that they always have some angle of attack relative to the wind. The main advantage to this design is that the torque generated remains almost constant over a fairly wide angle, so a Cycloturbine with three or four blades has a fairly constant torque. Over this range of angles, the torque itself is near the maximum possible, meaning that the system also generates more power. The Cycloturbine also has the advantage of being able to self-start, by pitching the "downwind moving" blade flat to the wind to generate drag and start the turbine spinning at a low speed. On the downside, the blade pitching mechanism is complex and generally heavy, and some sort of wind-direction sensor needs to be added in order to pitch the blades properly.
Helical blades
The blades of a Darrieus turbine can be canted into a helix, e.g. three blades and a helical twist of 60 degrees. The original designer of the helical turbine is Ulrich Stampa (Germany patent DE2948060A1, 1979). A. Gorlov proposed a similar design in 1995
(Gorlov's water turbines). Since the wind pulls each blade around on both the windward and leeward sides of the turbine, this feature spreads the torque evenly over the entire revolution, thus preventing destructive pulsations. This design is used by the
Turby,
Urban Green Energy
UGE International is a worldwide distributed solar energy company, founded in 2008, with headquarters in New York City and Toronto, and a local office in the Philippines. As of 2021, the company has installed 500MW of solar energy worldwide and c ...
,
Enessere, Aerotecture and
Quiet Revolution
The Quiet Revolution (french: Révolution tranquille) was a period of intense socio-political and socio-cultural change in French Canada which started in Quebec after the election of 1960, characterized by the effective secularization of govern ...
brands of wind turbine.
Active lift turbine
![Crank rod system](https://upload.wikimedia.org/wikipedia/commons/8/88/Crank_rod_system.png)
The relative speed creates a force on the blade. This force can be decomposed into an axial and normal force (Fig. 5). In the case of a Darrieus turbine, the axial force associated with the radius creates a torque and the normal force creates on the arm a stress alternately for each half turn, a compression stress and an extension stress. With a crank rod system (Fig. 6), the principle of the Active Lift Turbine is to transform this alternative constraint into an additional energy recovery.
[Lecanu, Pierre normandajc and Breard, Joel and Mouaze, Dominique]
''Operating principle of an active lift turbine with controlled displacement''
Jul 2018
References
External links
US patent 1,835,018Cranfield University press release on novel-configuration vertical-axis wind turbine for offshore generation Brief introduction to the theory of Darrieus wind turbines
{{Wind power
Vertical axis wind turbines
French inventions
20th-century inventions
fr:Éolienne#Axe vertical